There are a variety of types of optical information recording media, for example, an optical disk in which a cured film made of an active energy ray curable resin composition is formed on an information recording layer formed on a substrate in order to protect the information recording layer, or an bonded type optical disk in which two substrates provided with an information recording layer on at least one of them are bonded to each other using a cured film made of an active energy ray curable resin composition, etc.
An information recording layer refers to a laminate including a layer formed on an optical disk substrate made of a synthetic resin such as polycarbonate and constituted by an unevenness called a pit, a phase change material, coloring matter or the like, and a semi-transparent reflective film or a perfect reflective film formed on the above layer for reflecting a laser beam for reading information. The semi-transparent reflective film or the perfect reflective film is formed on the uppermost layer of the information recording layer and is typically constituted by a thin film made of a metal or metal alloy.
A typical example of the bonded type optical disk includes DVD (Digital Versatile Disk or Digital Video Disk). Among the bonded type optical disks, in DVDs, there are a variety of types of read-only DVDs. For example, an optical disk named “DVD-10” is manufactured by providing unevenness called a pit responsible to recording information on one side of a substrate; preparing for example, two polycarbonate substrates used for optical disk thereon as a layer for reflecting a laser beam for reading information, the substrate being provided with aluminum layers; and bonding the two polycarbonate substrates by adhering the aluminum layers as an adhesion layer. “DVD-5” is manufactured by bonding the substrate used to manufacture “DVD-10” and a normal transparent polycarbonate substrate without an information recording layer. “DVD-9” is manufactured by bonding a substrate in which an aluminum reflective film is formed on pits provided in one side of the substrate and a substrate in which a semi-transparent reflective film, which is made of gold or an alloy containing gold as a main component, silver or an alloy containing silver as a main component, a silicone compound, or the like, is formed on one side of the substrate by adhering the two reflective films as an adhesion layer. “DVD-18” is manufactured by bonding two substrates, each of which has one side having two information layers formed thereon. At present, “DVD-9” having large recording capacity and allowing two-layered information to be read from one side is being widely used.
DVD may be generally divided into a read-only type and a writable type. A writable DVD includes a recordable type such as DVD-R and DVD+R, and a rewritable type such as DVD-RW, DVD+RW and DVD-RAM. Among these DVDs, DVD-R and DVD+R of the recordable type have a characteristic that uses an organic coloring matter for a recording layer, unlike other DVDs. In a recordable type optical disk, the optical property is changed or unevenness is formed irreversibly by irradiating the substrate with a laser beam, thereby forming a recording layer. For the recording layer, for example, cyanine-based, phthalocyanine-based, and azo-based organic coloring matters, which are decomposed by heat from the laser beam irradiation, thereby changing the optical constant thereof and causing deformation of the substrate by the volume change, are used.
Although many of such methods have been developed, the optical disks using various recording methods developed in succession require in common that a signal written on an information recording layer should be stably read and that occurring of signal reading error should be highly suppressed. In recent years, in particular, since spots such as fingerprints adhered to a surface of a polycarbonate substrate through which a laser beam passes scatter the laser beam, thereby making it impossible to read a signal written on an information layer, it has been studied to form a protective layer on the surface of the polycarbonate substrate to facilitate removal of spots.
As one of measures against the above problem, there has been proposed a method in which a non-crosslinked fluorine-based surfactant is mixed in a hard coating agent (see Patent Document 1). However, this method can not achieve a spot prevention function sufficiently since the fluorine-based surfactant is present only in a portion of a surface of the protective layer, and therefore requires further improvement. In addition, since the fluorine-based surfactant is merely mixed in the hard coating agent, there may arise a problem of deterioration of the spot prevention function after lapse of a long period of time or when the protective layer is left under a high-temperature and high-humidity circumstance.
For an optical recording disk having an excellent fingerprint wipe-ability, there has been disclosed an optical recording disk having a jitter rise rate of not more than 1.15 times when sticking and wiping out an adhered artificial fingerprint liquid (see Patent Document 2). This document discloses that the hard coat layer includes an active energy ray curable silicone-based compound in order to provide an excellent water-repellency and lubricity. However, in this document, the disclosed silicone-based compounds are merely enumerated without being specified to attain an optical recording disk having a jitter rise rate of not more than 1.15. Although this document discloses an example employing polydimethylsiloxane having reactive acrylolyl group at its end, it is difficult for this compound to prevent spots and obtain spot wipe-ability, therefore further improvement is required. In addition, many of the enumerated silicone-based compounds insoluble with an acrylate-based polymerizable monomer forming a hard coat layer, and, if used, require a solvent which should be removed in a later process of forming a coating film.
[Patent Document 1] Japanese Patent Unexamined Application, First Publication No. Hei 10-110118
[Patent Document 2] Japanese Patent Unexamined Application, First Publication No. 2004-335021